B cells are produced by and develop in bone marrow. During development, B cells progress through central tolerance checkpoints, rendering them non-self reactive. Central tolerance mechanisms include 1) clonal deletion, where B cells that recognize “self” (body antigens) are destroyed by apoptosis and 2) receptor editing where modifications in the B cell receptor are made to render the B cell no longer self reactive.
Throughout B cell development, signals transduced through the B cell antigen receptor (BCR) play an important role in regulating B cell maturation (Basten, A. R. et al. 1991. Immunol. Rev, 122:5; Nemazee, D. et al. 1991. Immunol. Rev, 122:117). However, BCR-induced signals can lead to dramatically different functional responses, depending on the maturational stage of the B cell. For instance, although both immature and mature B cells express the mature antigen-binding form of the BCR, immature B cells undergo negative selection, or are tolerized, in response to receptor ligation, while mature B cells are induced to proliferate and secrete immunoglobulin (Ig). Immature B cells in the bone marrow that have just begun to express surface IgM, as well as late-immature or transitional-stage B cells that have recently emigrated from the bone marrow to the spleen and that express high levels of surface IgM and low levels of surface IgD, are sensitive to this tolerization process (Carsetti, R. et al. 1995. J. Exp. Med. 181:2129; Allman, D. M. et al. 1992. J. Immunol. 149:2533; Allman, D. M. et al. 1993. J. Immunol. 151:4431). The sensitivity of immature B cells to tolerization following antigenic exposure is believed to be critical for the maintenance of immunological self-tolerance. Immature B cells are believed to be tolerized by a number of mechanisms including clonal anergy (Gooclnow, C. C. et al. 1988. Nature 334:676), receptor editing (Gay, D. et al. 1993. J. Exp. Med. 177:999), competition for follicular niches (Cyster, J. G. et al. 1994. Nature 371:389) and clonal deletion (Hartley, S. B. et al. 1993. Cell 72:325).
B cells undergo a random process of V(D)J recombination in order to generate the many distinct receptors needed to recognize a vast array of antigens. An inevitable consequence of this random process is the production of autoreactive B cells (Wardemann et al., 2003, Science 301(5638):1374-7). An important mechanism for tolerizing autoreactive B cells is receptor editing (Halverson et al., 2004, Nat Immunol 5(6):645-650). Receptor editing results in the alteration of B cell receptor specificity and is achieved by ongoing immunoglobulin (Ig) gene rearrangement, most commonly at the light chain loci (Gay et al., 1993, J Exp Med. 177(4):999-1008; Tiegs et al., 1993, J Exp Med. 177(4):1009-20; Radic et al., 1993, J Exp Med. 177(4):1165-73). Light chain rearrangement proceeds in an ordered fashion as B cells develop in the bone marrow, with κ genes recombining first, followed by rearrangement of the Recombining Sequence and λ (Lewis et al., 1982, Cell 30(3):807-816; Muller et al., 1988, J Exp Med. 168(6):2131-2137). The Recombining Sequence (known as the Kappa Deleting Element (KDE) in humans, hereafter RS) is a non-coding gene segment located 25 kb downstream of Cκ in the κ locus that is rearranged during continued Ig light chain gene rearrangement (Durdik et al., 1984, Nature 307(5953):749-752; Siminovitch et al., 1985, Nature 316(6025):260-262).
The recombining sequence (RS) of mouse and its human equivalent, the immunoglobulin (Ig) kappa deleting element (IGKDE), are sequences found at the 3′ end of the Ig kappa locus (Igκ) that rearrange to inactivate Igκ in developing B cells. RS recombination correlates with Ig lambda (Igλ) light (L) chain expression and likely plays a role in receptor editing by eliminating Igκ genes encoding autoantibodies.
Systemic lupus erythematosus (SLE) is a chronic, inflammatory autoimmune disease characterized by the production of autoantibodies having specificity for a wide range of self-antigens. SLE autoantibodies mediate organ damage by directly binding to tissues and by forming immune complexes that activate immune cells. Organs targeted in SLE include the skin, kidneys, vasculature, joints, various blood elements, and the central nervous system (CNS). The severity of disease, the spectrum of clinical involvement, and the response to therapy vary widely among patients. This clinical heterogeneity makes it challenging to diagnose and manage lupus.
IDDM (Insulin-Dependent Diabetes Mellitus) otherwise known as Type 1 diabetes is another example of an autoimmune disease in which there is a need for better diagnostic assays. Three major theories have been advanced to account for the pathogenesis of the disease. The first is that IDDM is an inherited, or genetic disease. The second is that IDDM results from autoimmunity. The third theory states that IDDM is brought about by an environmental insult, presumably viral (Cotran, 1989 Robbins Pathologic Basis of Disease 994-1005; Foster, 1991 Harrison's Principles of Internal Medicine 1739-1759). Most agree that it is a combination of elements of all three theories that eventuates in IDDM, rather than each of the three acting independently in different individuals.
IDDM results from destruction of the insulin-producing 3-cells of the pancreatic islets. Without insulin, glucose is not effectively taken up into such metabolically active tissues as muscle, liver or adipose tissue. The result is hyperglycemia. The hyperglycemia present in IDDM is thought to contribute to the major pathologies associated with the disease, such as those found in the peripheral nerves, retina, kidney, and vasculature.
Perhaps the most widely accepted therapy for treating IDDM involves daily injection of insulin in combination with blood glucose monitoring and eating behavior modification, indirectly reducing undesirable secondary side effects and the risk of life-threatening complications. Moreover, alternative therapies including pancreas and islet transplantation, autoantigen-based therapies (e.g., glutamic acid decarboxylase (GAD) therapy), and β cell-related peptide adjunctive therapies are being developed and tested.
There exists a need for new diagnostic tools aimed at identifying persons having or who are predisposed to diseases such as SLE or IDDM. The present invention addresses this need.